The last two articles explained two bad options. One is to peek freely and inflate your false-positive rate. The other is to lock yourself into a single fixed-horizon check and lose the ability to react early entirely — whether that means shipping a good result sooner or rolling back to what you had before. Group Sequential Testing (GST), the framework introduced today, offers a third option: look several times, on a plan you commit to in advance, while keeping your error probability controlled within 5%.
What Group Sequential Testing Actually Is
Group Sequential Testing refers to any experiment design where you pre-specify a small number of interim checks — "looks" — at planned points during data collection...